1. Field of the Invention
The present invention relates to a mass spectrometer.
2. Description of Related Art
A quadrupole mass spectrometer is a mass spectrometer for detecting the intensities of ions of desired mass-to-charge ratios by applying an RF voltage and a DC voltage to a hyperbolic quadrupole mass filter (QMF) and passing only the ions of the desired mass-to-charge ratios. There are two analysis modes: scan mode in which the desired ion mass-charge-ratio is scanned continuously; and single ion monitoring (SIM) mode in which the mass-to-charge ratio is held constant. In the SIM mode, the accumulation time for one type of ion is long and a high sensitivity is obtained and, therefore, this mode is used in many quantitative measurements. Furthermore, in a triple quadrupole mass spectrometer (TQMS) in which two quadrupole mass filters are connected, the specificity and quantitativeness are improved compared with a single quadrupole mass spectrometer. Therefore, TQMS has been frequently used for structural analysis and quantitative analysis in recent years. See the following prior art: U.S. Pat. Nos. 4,963,736, 5,248,875, and 6,111,250.
In a quadrupole mass spectrometer or a triple quadrupole mass spectrometer, in a case where ions to be selected by the quadrupole mass filter of the mass analyzer are varied, some time is required to modify the RF voltage and DC voltage applied to the quadrupole mass filter. In the conventional quadrupole mass spectrometer or triple quadrupole mass spectrometer, ions generated by the ion source are continuously transported to the detector and so ions pass into the mass analyzer while the voltages are being modified. However, these ions cannot reach the detector or, if they reach the detector, the mass-to-charge ratios cannot be identified and thus the detector output signal is discarded. This presents the problem that ion loss occurs.